1. Field of the Invention
The present invention relates to thin film transistors (hereinafter referred to as xe2x80x9cTFTsxe2x80x9d), a liquid crystal display device and an electronic apparatus using an active matrix substrate provided with driving circuits including the TFTs. In particular, the present invention also relates to structural techniques for enhancing an efficiency of heat radiation from the TFTs.
2. Description of Related Art
TFTs and a TFT circuit widely used as an active matrix substrate for a liquid crystal display device are formed so that, as shown in FIG. 14 and FIG. 15, gate electrode 15Q, source-drain region 12Q and channel region 17Q each have an almost rectangular plane shape without extending in its side direction. In addition, in each TFT 1Q in FIG. 15, silicon films forming source-drain region 12Q and channel region 17Q are patterned in an independent insular shape. Here, when various types of TFT circuits are formed from TFTs, a wiring layer 801Q formed to have a uniform width is used to mutually connect the TFTs.
In a TFT circuit having a conventional structure, increasing the current flowing in the TFT 1Q in order to improve its characteristics and performance increases the temperature of the channel region 17Q due to the self-heating of the TFT 1Q, which causes problems such as deterioration in the characteristics and a decline in reliability.
Accordingly, there can be proposed a method for suppressing the temperature rise of the TFT by providing a high thermal-conducting layer between layers included the TFT 1Q and using it as a heat-radiating layer. This method however has a problem in which, when an active matrix substrate or the like is produced, the step of forming a film used as a heat-radiating layer, and the step of patterning the film are added. Such additional production steps are undesirable because they increase the production cost.
In FIG. 14 and FIG. 15 showing the related art, the contact hole 19 is formed in each source, drain and gate region having a uniform width. When one side of the contact hole is larger than each source, drain or gate region, there may be a case in which each region is enlarged more than the uniform-width portion only around the contact hole, which, however, does not consider the heat radiation characteristics and results in no improvement thereof.
In view of the foregoing problems, an object of the present invention is to provide: a TFT circuit having a structure for enhancing the heat radiation efficiency without increasing the number of production steps, in which its characteristics do not deteriorate and its reliability does not decline; and a liquid crystal display device provided with an active matrix substrate using the TFT circuit as a driving circuit.
In order to solve the foregoing problems, the present invention provides: a TFT including on the surface side of a substrate a channel region opposed to a gate electrode, with a gate insulating film provided therebetween, and a source-drain region connected to the channel region; and a TFT having a source-drain wiring layer electrically connected to the source-drain region, and a gate wiring layer electrically connected to the gate electrode, in which at least one component part composed of a conductive film or a semiconductor film, among the component parts of each thin film transistor, is provided with a heat-radiating extension.
In other words, not by adding a new layer to TFTs, but by enlarging part of each component of the TFTs, the heat-radiating efficiency from the TFTs is enhanced.
According to the present invention, a heat-radiating extension is provided on at least one component composed of a conductive film or a semiconductor film among the components of the TFTs. Thus, in the plan view, the area capable of radiating heat is enlarged. Also, providing the extension enlarges the areas of side portions. In other words, the heat-radiating efficiency from the component is increased by the amount of the enlarged surface area thereof. In addition, the heat-radiating extension is composed of a film having a thermal conductivity higher than that of an insulating film such as a conductive film or a semiconductor film, which enables efficient heat radiation from the extension. Moreover, the heat-radiating extension is a portion extended from one component originally included in the TFTs. Accordingly, even when the heat-radiating extension is provided, the number of production steps cannot be increased. Therefore, the production cost of the TFT does not increase.
According to the present invention, the heat-radiating extension may be formed as a portion extending from the gate electrode at both sides.
For example, the extending portion of the gate electrode may be provided on at least one end of the gate electrode. In this case, it is preferable that the gate wiring layer is electrically connected to the extending portion of the gate electrode by a plurality of contact holes. This arrangement enables efficient heat conduction from the gate electrode to the gate wiring layer, which enhances the radiating efficiency.
In addition, the extending portion of the gate electrode may be provided in a region opposed to the channel region. This arrangement prevents the extending portion of the gate electrode from projecting out of the region where the TFT is formed, which does not hinder the high integration of the TFT. In this case, it is preferable that the extending portion of the gate electrode is provided at a location corresponding to an approximately central region in the width of the channel region. This arrangement increases the radiating efficiency of the portion of the channel width in which heating is remarkable, which enhances the effect thereof.
According to the present invention, the heat-radiating extension may be formed as a portion extending from the channel region at both sides. In this case, it is preferable that the extending portion of the channel region is provided in a region opposed to the gate electrode. This arrangement prevents the extending portion of the channel region from projecting out of the region where the TFT is formed, which does not hinder the high integration of the TFT.
According to the present invention, the heat-radiating extension may be formed as a portion extending from the source-drain region to both sides. In this case, it is preferable that the source-drain wiring layer is electrically connected to the extending portion of the source-drain region by a plurality of contact holes. This arrangement enables efficient heat conduction from the source-drain region to the source-drain wiring layer, which enhances the radiating effect.
According to the present invention, the heat-radiating extension may be formed as an extending portion extended from the source-drain region at both sides so that, in a CMOS inverter circuit including the thin film transistors, which are an inversely conductive type, the adjacent source-drain regions of the thin film transistors are connected between CMOS circuits. In this case, it is preferable that the heat-radiating extension is provided with conductivity by using an impurity identical to the impurity of the source-drain region to which the extension itself is connected. This structure causes the radiating extension itself to show the function of redundant wiring. In addition, it is preferable that the radiating extension is formed in a region opposed to the source-drain wiring layer for connecting the adjacent source-drain regions of the thin film transistors between the CMOS circuits. This structure prevents the radiating extension from projecting out of the source-drain interconnection layer, which does not hinder the high integration of the CMOS inverter circuit.
According to the present invention, the heat-radiating extension may be formed as an extending portion from at least either of the source-drain wiring layer and the gate wiring layer at both sides.
The TFTs in which the heat-radiating efficiency is increased in the above manner are suitable for forming a driving circuit on an active matrix substrate for a liquid crystal display device.